Do different colors have different intensities?

Question

I did a biology lab on crickets and their behavior towards light and shaded areas. Crickets, being nocturnal, naturally tended to go toward the shaded areas. We then manipulated the experiment to see if different colored filters of light (yellow, green, purple, red) changed their behavior. Our results were that in yellow, more crickets were in the shaded area. In green, more crickets were in the green light. In purple, more crickets were in the purple light, and in red light, more crickets were in the red light. I can't think of any way to explain this and was thinking that maybe different colors had different intensities... Any help or clarification would be great!

Answer 1

They don't have different "intensity" but they do have different "brightness". This sounds weird, but it has to do with the precise definition of the words "intensity" and "brightness".

The intensity is the *amount* of light hitting the eye. If you know about photons, it is the *number* of photons being pumped out by the light source. The intensity is completely independent of the color (the frequency of the photons). If you have a colored lamp with a dimmer knob. You can increase or decrease the intensity (increase the number of photons it is pumping out), but this will not change its color.

The brightness is how the eye *responds* to the light. Eyes are more sensitive to some colors than to others. For example, the human eye responds very well to yellow, and less well to blue, and not at all well to purple. So if you have three lamps of the same intensity (all putting out the same numbers of photons), but one is yellow, one blue, one purple ...TO HUMANS, yellow light looks brighter than blue light, and purple light looks much dimmer.

The same will be true of the crickets, although I don't know off the top of my head what their color range is.

But brightness is also dependent on intensity. If you have three lamps of the same color, but different intensities, the higher the intensity, the higher the brightness. This would be true of both humans and crickets.

So if the crickets move away from the yellow light more than, say, the purple light, then this would mean either:
(a) The yellow light actually had a brighter intensity, than the purple light; or
(b) Cricket eyes are more responsive to yellow light than to purple light (which is similar to humans).

To eliminate (a) you would need to *calibrate* your lamps to the same intensity. I don't know how you would do that as I don't know what equipment you have. Perhaps a photographer's light meter would do that.

It would not make sense to me that the crickets would *ever* move out of the shade into the light, regardless of what color the light is. The shadows are always darker.

So they should always move towards shadows but will do so *faster* with the colors of light they are more sensitive to ... or they may not move at all if their eyes can't see the light at all. So I would measure the *speed* at which they move towards the shadows (how many minutes does it take for them to gather in the shadows).

--- p.s. ----

'seemynewname' also has a great point. You also have to consider the possibility that the lamps are close enough to be pumping out heat.

In fact, if the crickets seem to be moving *into* the lit areas with certain colors, this might indicate that the light is perceived by them as heat energy (and they're attracted to it), but not visible energy (which they don't like). You might want to do some experiments where you heat parts of the cage using a small heater under the (rather than light) to see if they are indeed attracted or repelled by heat.

Answer 2

Light is a form of electromagnetic radiation, the part of the spectrum which is visible light; colors therefore differ in their wavelengths, red having the shortest wavelength, then orange, yellow, green, blue, indigo, and violet having the longest. It is an interesting experiment, and if your white light source was constant, then your filters in the darker colors would actually absorb more of the light, so that the brighter colors would indeed be more intense. It would seem to follow then that the crickets preferred the less bright environments, the darker colors of the spectrum.

Answer 3

two possibilities here
1. you changed the HEAT output and they went to the cooler area
2. crickets do not see in the same frequency as humans so they perceived the place they went as the one with the least LIGHT
I would go with 1 just because shade is the preferred environment - you can easily find out by measuring the SURFACE TEMP of each area

Answer 4

objectively color is different from intensity. subjectively, it depends on what and which sensor whether eye or optic and its sensitivity to which wavelength

Answer 5

yes they do just like a bull seeing red